Major Report Reasserts Link Between Rising Temperatures, Fossil Fuels; Warns of a Tipping Point With Severe Effects

STOCKHOLM—A landmark United Nations report issued Friday reaffirmed the growing belief that human activity is the dominant cause behind a rise in global temperatures and reiterated that a long-term planetary warming trend is expected to continue.

The report could have a significant impact on policy-making because it underscores that human activity is pushing atmospheric carbon-dioxide concentrations toward levels whereby the surface temperatures may increase by 2 degrees Celsius. Many governments have pledged to try to...